Study On Self-propagating Synthesis And Its Stability Of PbSe

In today's world,energy crisis and environmental pollution are two difficult problems to be solved urgently.The exploration of new sustainable and clean energy such as nuclear energy has become a research hotspot.Thermoelectric materials have attracted wide attention because they can realize the direct conversion of thermal energy and electric energy,and have no pollution,no vibration,high reliability and no maintenance.It is a hot field to explore efficient thermoelectric materials to solve the energy crisis.Thermoelectric technology can be combined with radioisotope sources to make power generation devices for power generation,and can be used to supply energy in a variety of extreme environments,such as radioisotope thermoelectric battery(RTG)in the field of aviation.At present,the thermoelectric material used in radioisotope thermoelectric battery is mainly Pb Te,although its application in aviation field is relatively mature,but the scarcity of raw materials,high price,tedious material synthesis process,time-consuming and other problems hinder its further large-scale commercial process.As a sister material of Pb Te,PbSe has good intrinsic electrical and thermal properties,and it is also chalcogenide,and its physicochemical properties are similar.In addition,Te/Ge is scarce in the earth's crust,while Se is rich in elements,so PbSe is expected to replace Pb Te,as an alternative material for a new generation of RTG.In this paper,a kind of ultrafast synthesis method-high temperature self-propagating synthesis reaction is adopted to realize the rapid preparation of PbSe-based thermoelectric materials,and an effective strategy of morphological engineering design is introduced in combination with Ag doping.This strategy can be used to break through the obstacles of PbSe to obtain high power factor and low thermal conductivity at the same time.Through excessive Ag doping and ultra-fast synthesis process,a large number of Ag₂Se nanofibers are precipitated in the material.The parallel connection established in the Ag-doped PbSe material can effectively improve the comprehensive electrical properties,with lower effective mass and higher hole mobility.Meanwhile,a large number of multi-size pores were formed during the violent reaction,which enhanced phonon scattering,decreased sound velocity and phonon average free path(MFP),and further reduced the lattice thermal conductivity of Ag-doped materials.Finally,for p-type PbSe,it has a higher thermoelectric merit value(z T)?1.2 at 773 K and an average z T value of?1.1 between 523 K-823 K.In addition,since the synthesis reaction of PbSe is reversible,and its elemental composition include high vapor pressure element Se,and its working environment temperature is high.Therefore,we carried out high temperature operation experiments to explore the changes of its stability under some operating conditions(including working time,temperature and atmosphere),and tried to improve its stability by spraying boron nitride protective layer on its surface.We found that the instability of PbSe material was obvious at high temperature,due to the non-equilibrium process of reaction and the high vapor pressure element Se.So that its degradation behavior is inevitable even in vacuum environment.In addition,when running at high temperature in the air environment,the surface is easy to be oxidized and lead to material failure.At 723 K,the oxide layer will be formed on the surface after heat treatment for more than 24 h,and there are elements missing,which leads to the decline of properties.Spraying a certain thickness of BN in vacuum and air environment cannot inhibit the high temperature degradation behavior of PbSe.In the air environment,the thermal expansion coefficient of the two materials does not match,which leads to cracks in the BN protective layer at high temperature,which leads to the infiltration of oxygen.Therefore,spraying BN with a thickness of?25?m can only slightly inhibit the oxidation behavior of PbSe at high temperature.This work points out the direction for the stability protection of PbSe materials in the future.Combined with the energy-saving and time-saving characteristics of PbSe prepared by our method,we can see the broad prospect of the application of PbSe-based thermoelectric materials in RTG and other scenarios in the future..